In cognitive psychology, fast mapping is a mental process whereby a new concept can be learned (or a new hypothesis formed) based only on a single exposure to a given unit of information. Fast mapping is particularly important during language acquisition in young children, and serves (at least in part) to explain the prodigious rate at which children gain vocabulary.

Fast mapping derives its power from the formation of tentative working hypotheses. For example, in a group of mostly familiar items with one novel item and a novel word, an individual will quickly associate the new word with the novel item. Over time the word's approximate meaning becomes more refined as it is seen in other contexts.

The phenomenon was first formally observed, and the term fast mapping coined, by Harvard researchers Susan Carey and Elsa Bartlett in 1978.